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This article explains the life cycle of Application State; the Global.asax file is alsoexplained with a real-life example.

Application State in ASP.NetBy Divya Sharma on Jun 15, 2014

Download Files: Application_state.rar

Background

We all know that the web uses the HTTP protocol and that the HTTP protocol is a stateless protocol, in otherwords when a client sends a request to the server, an instance of the page is created and the page isconverted to HTML format and then the server returns the response and then the instance of the page andthe value of the control is destroyed. So if we have a requirement to store the value of controls then a StateManagement technique is used.

Introduction

Application State is a state management technique. Application State is stored in the memory of the theserver and is faster than storing and retrieving information in a database. Session sate is specific for a singleuser session, but Application State is for all users and sessions. Application State does not have a defaultexpiration period. When we close the worker process the application object will be lost. Technically the data isshared amongst users by a HTTPApplcationState class and the data can be stored here in a key/value pair. Itcan also be accessed using the application property of the HTTPContext class.

Application State Life Cycle

Step 1 : When the Browser sends a request to the web server and the server receives the the request it firstchecks the extension to determine whether or not it is ISAPI because this request can only be handled bythe ISAPI extension; if the extension is different then the request is handled by the server itself.

Step 2 : After receiving the request the Application Manager creates an application domain. In theapplication domain an instance of the class HostingEnvironment is created that provides access toinformation about all application resources.

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Step 3 : After creating the application domain, ASP.NET initializes the basic objects as HTTPContext,HTTPRequest and HTTPResponse. HTTPContext holds objects to the specific application request asHTTPRequest and HTTPResponse.HTTPRequest contains all the information regarding the current requestlike cookies, browser information and so on and the HTTPResponse contains the response that is sent to theclient.

Step 4 : Here all the basic objects are being initialized and the application is being started with the creationof the HTTPApplication class.

Step 5 : Then events are executed by the HTTPApplication class for any specific requirement. Here is a list ofevents:

Global.asax file: the Global.asax file is used for handling application events or methods. It always exists inthe root level. Events are one of the following of the 2 types in the Global application:

1. Events that will be raised on a certain condition.2. Events that will be raised on every request.

The application will be started only once; if 10 users send a request then 10 user sessions are created. Theevents of the Global.asax file are:

1. Application_Start : This method is invoked initially when first application domain is created.2. Session_Start : This method is called every time a session is start.3. Application_BeginRequest : After an application has started the first method

Application_BeginRequest is executed for every user.4. Application_AuthenticateRequest : It checks to determine whether or not the user is valid.5. Application_Error : Whenever an unhandled exception occurs then this event will be called.6. Session_End : When a user session is ended and all the data related to a specific user is cleared then

the Session_End event is called.7. Application_End : This method is called before the application ends. This can take place if IIS is

restarted or the application domain is changing.8. Application_Disposed : This event is called after the application will be shut down and the .NET GC

is about to reclaim the memory it occupies. Although this is very late to perform any cleanup but wecan use it for safety purposes.

ASP.NET Application State reallife example

Now I am explaining the reallife example. If you want to see the number of users online then we need touse Application State.

Step 1 : Open Visual Studio 2010.

Step 2 : Then click on "New Project" > "Web" > "ASP.NET Empty Web Application" .

Step 3 : Now click on Solution Explorer.

Step 4 : Now rightclick on "Add" > "New Item" > "Web Form" and add the name of the web form.

Step 5 : Now add the Global.asax file. Again go to Solution Explorer and "Add" > "New Item" > "GlobalApplication Class".

Step 6 : Now to configure the session we need to use the web.config file as in the following:

01.

Step 7 : Now to count the number of users online we need to use the global.asax file as in the following:

01. protectedvoidApplication_Start(objectsender,EventArgse)02. {03. //thiseventisexecuteonlyoncewhenapplicationstartanditstorestheservermemoryuntiltheworkerprocessisrestart04. Application["user"]=0;05. }06. protectedvoidSession_Start(objectsender,EventArgse)07. {08. //whensessioninstartapplicationvariableisincreasedby109. Application.Lock();10. Application["user"]=(int)Application["user"]+1;11. Application.UnLock();12. }13. protectedvoidSession_End(objectsender,EventArgse)14. {15. //whensessioninendapplicationvariableisdecreaseby116. Application.Lock();17. Application["user"]=(int)Application["user"]1;18. Application.UnLock();19. }

Step 8 : Now to show the online users we need to use a web form as in the following:

01. protectedvoidPage_Load(objectsender,EventArgse)02. {03. Response.Write("Thenumofusersonline="+Application["user"].ToString());04. }

Output

When the same request is sent to the server with a different browser then the number of online clients isalso not increased because the browser binds with the session id so both of the tabs have the same sessionid so the server knows that the request comes from the same user. If we change the session id from the URLand again refresh then the number of online clients is increased by one because the server thinks that therequest comes from a different browser.

Important points of Application State variables

1. Application State variables are available across all pages and all sessions. Application State variablesare like multiuser Global data.

2. Application variables are stored on a web server.3. Application State variables are cleared, only when the process hosting the application is restarted, that

is when the application is ended.4. Application State variables do not support web farms and web gardens: Application State variables are

not supported be web farms.

A client sends a request and the request goes to the load balancer and the load balancer sends arequest to web server1 and the Application State variables are stored in a web server1. If thesubsequent request is sent by the client again and the load balancer sends a request to web server2and the Application State variables are not stored in web server2 then something. Web servers do notshare application state variables.

5. Application State variables have a concurrency problem so we need to synchronize the method byusing the lock and unlock methods. So multiple thread problems are resolved since only one threadcan do the work.

6. An application variable is used only when the variable needs to have global access and when you needthem for the entire time, during the lifetime of an application.

Divya SharmaHello I am Divya Sharma,Now i am final year student of mewar university,chittorgarh(Rajasthan)

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COMMENTS 1of1

Jan 23, 2015

620 7 1.8k 1 0 Post Reply

Nice article ...Deepak Porwal

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